#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

//template
#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
using ll=long long int;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

template<typename M,typename N
   ,M (*f)(M,M),M (*g)(M,N),N (*h)(N,N)>
class LazySegmentTree{
   int sz,height; vector<M> data; vector<N> lazy;
   const M m1; const N n1;
   M ref(int k){return g(data[k],lazy[k]);}
   void recalc(int k){while(k>>=1)data[k]=f(ref(2*k),ref(2*k+1));}
   void thrust(int k){for(int i=height;i>0;i--)eval(k>>i);}
   void eval(int k){
      lazy[2*k]=h(lazy[2*k],lazy[k]); lazy[2*k+1]=h(lazy[2*k+1],lazy[k]);
      data[k]=ref(k); lazy[k]=n1;
   }
public:
   LazySegmentTree(int n,const M &m1,const N n1):m1(m1),n1(n1){
      sz=1,height=0; while(sz<n)sz<<=1,height++;
      data.assign(2*sz,m1); lazy.assign(2*sz,n1);
   }
   void run(vector<M>& v){
      rep(i,0,v.size())data[i+sz]=v[i];
      for(int k=sz-1;k>0;k--)data[k]=f(data[2*k],data[2*k+1]);
   }
   void set(int a,M x){thrust(a+=sz); data[a]=x; recalc(a);}
   void update(int a,int b,N x){
      if(a>=b)return;
      thrust(a+=sz); thrust(b+=sz-1);
      for(int l=a,r=b+1;l<r;l>>=1,r>>=1){
         if(l&1)lazy[l]=h(lazy[l],x),++l;
         if(r&1)--r,lazy[r]=h(lazy[r],x);
      }
      recalc(a); recalc(b);
   }
   M query(int a,int b){
      if(a>=b)return m1;
      thrust(a+=sz); thrust(b+=sz-1);
      M L=m1,R=m1;
      for(int l=a,r=b+1;l<r;l>>=1,r>>=1){
         if(l&1)L=f(L,ref(l++));
         if(r&1)R=f(ref(--r),R);
      } return f(L,R);
   }
};

int f(int a,int b){return min(a,b);}
int g(int a,int b){return (b==inf/2?a:b);}
int h(int a,int b){return (b==inf/2?a:b);}

int main(){
   int n,q;
   cin>>n>>q;
   LazySegmentTree<int,int,f,g,h> seg(n,inf/2,inf/2);
   using T=array<int,3>;
   vector<T> a(q);
   rep(i,0,q){
      cin>>a[i][1]>>a[i][2]>>a[i][0];
      a[i][1]--;
   }
   sort(ALL(a));
   for(auto& xyz:a){
      seg.update(xyz[1],xyz[2],xyz[0]);
   }
   for(auto& xyz:a){
      if(seg.query(xyz[1],xyz[2])!=xyz[0]){
         puts("-1");
         return 0;
      }
   }
   rep(i,0,n){
      int ret=seg.query(i,i+1);
      cout<<ret<<(i==n-1?'\n':' ');
   }
   return 0;
}